Lighting apparatus with a plurality of light engines

ABSTRACT

A LED based lighting apparatus is disclosed. The light engine used in the lighting apparatus may use printed circuit board and have a plurality of LED groups that are independently controllable by a control unit. The power supply input and return paths connected to each LED group may be implemented on different layers to allow a compact footprint that may be used with traditional fluorescent encasements with relatively little modification. The LEDs may comprise a subset of LEDs having a first colour and a subset of LEDs having a second colour different from said first colour intertwined on the light engine.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation of and claims the benefitunder 35 USC 120 of U.S. patent application Ser. No. 15/919,147 entitled“LIGHT ENGINE AND LIGHTING APPARATUS WITH FIRST AND SECOND GROUPS OFLEDS” by Briggs filed on Mar. 12, 2018, which is a continuation of andclaims the benefit under 35 USC 120 of U.S. patent application Ser. No.15/426,049 entitled “CONTROL UNIT AND LIGHTING APPARATUS INCLUDING LIGHTENGINE AND CONTROL UNIT” by Briggs filed on Feb. 6, 2017, which claimsthe benefit under 35 USC 120 of U.S. patent application Ser. No.15/136,599 entitled “LED LIGHTING APPARATUS WITH FIRST AND SECOND COLOURLEDS” by Briggs filed on Apr. 22, 2016, which claims the benefit under35 USC 120 of U.S. patent application Ser. No. 14/606,013 entitled“MODULAR LED STRIP LIGHTING APPARATUS” by Briggs filed on Jan. 26, 2015,which claims the benefit under 35 USC 120 of U.S. patent applicationSer. No. 13/423,142 entitled “MODULAR LED STRIP LIGHTING APPARATUS” byBriggs filed on Mar. 16, 2012 which claims the benefit under 35 USC119(e) of U.S. Provisional Patent Application 61/467,914 filed on Mar.25, 2011 and hereby incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates generally to a lighting apparatus, andmore particularly to a lighting apparatus comprising a plurality oflight emitting diodes.

BACKGROUND OF THE INVENTION

Fluorescent lighting systems are widely used and many fluorescentlighting systems are designed to accommodate long slender fluorescenttubes.

Recently, lighting systems employing light emitting diodes (LEDs) haveincreased in popularity. LED based lighting systems may be moreefficient, have a longer lifespan, and be more controllable (e.g.colour, colour temperature) compared to traditional fluorescent lightingsystems. However, many existing LED based lighting systems generate arelatively large amount of heat and certain LED based lighting systemsrequire a large number of LEDs to achieve a desired lumen output. Thesefactors may limit the layout of LEDs in LED based lighting systems andmake it relatively difficult to modify the encasements used influorescent lighting systems for use with LEDs.

The present invention aims to mitigate at least one of the shortcomingsof prior art lighting systems.

SUMMARY OF THE INVENTION

In an embodiment of the invention there is provided a light enginecomprising: a printed circuit board; and a plurality of LED groups onsaid printed circuit board coupled between a power supply input and arespective one of a plurality of return paths associated with said LEDgroup; each of said LED groups comprising a plurality of LED setscoupled in parallel; each of said LED sets comprising a plurality ofLEDs coupled in series; wherein a first one of said LED groups iscomprised of at least a subset of LEDs having a first colour, and asecond one of said LED groups is comprised of at least a subset of LEDshaving a second colour different from said first colour; wherein atleast one of said LEDs having a first colour from said first LED groupand at least one of said LEDs having a second colour from said secondLED group are intertwined on said light engine.

In another embodiment there is provided a light engine comprising: aprinted circuit board; and a plurality of LED groups on said printedcircuit board coupled between a respective one of a plurality of powersupply inputs associated with said LED group and a return path; each ofsaid LED groups comprising a plurality of LED sets coupled in parallel;each of said LED sets comprising a plurality of LEDs coupled in series;wherein a first one of said LED groups is comprised of at least a subsetof LEDs having a first colour, and a second one of said LED groups iscomprised of at least a subset of LEDs having a second colour differentfrom said first colour; wherein at least one of said LEDs having a firstcolour from said first LED group and at least one of said LEDs having asecond colour from said second LED group are intertwined on said lightengine.

In another embodiment of the invention there is provided a lightingapparatus comprising: an optics section; and at least one light enginecomprising: a printed circuit board; and a plurality of LED groups onsaid printed circuit board coupled between a power supply input and arespective one of a plurality of return paths associated with said LEDgroup; each of said LED groups comprising a plurality of LED setscoupled in parallel; each of said LED sets comprising a plurality ofLEDs coupled in series; wherein a first one of said LED groups iscomprised of at least a subset of LEDs having a first colour, and asecond one of said LED groups is comprised of at least a subset of LEDshaving a second colour different from said first colour; wherein atleast one of said LEDs having a first colour from said first LED groupand at least one of said LEDs having a second colour from said secondLED group are mounted so that the light emitted from said LEDs overlapsbefore reaching the optics section of said lighting apparatus.

Other aspects and features of the present invention will become apparentto those of ordinary skill in the art upon review of the followingdescription of specific embodiments of the invention in conjunction withthe accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

In the figures which illustrate by way of example only, embodiments ofthe present invention,

FIG. 1 is a schematic diagram illustrating the layout of one layer of anembodiment of the invention;

FIG. 2 is a schematic diagram illustrating the layout of another layerof the embodiment of the invention shown in FIG. 1;

FIG. 3 is a schematic diagram illustrating the layout of an embodimentof a LED set in greater detail;

FIG. 4 is a schematic diagram of an alternative embodiment of a LED set;

FIG. 5 is a schematic diagram of a lighting apparatus comprised ofmultiple light engines;

FIG. 6 is a schematic diagram of an embodiment of a control unit ingreater detail;

FIG. 7 is a schematic diagram illustrating one possible arrangement ofLED groups and LED sets; and

FIG. 8 is a schematic diagram of an embodiment of a pass through boardthat may be used in certain embodiments of the invention.

DETAILED DESCRIPTION

The layout of LEDs in many LED based lighting systems may be limited bythermal management issues and ensuring that enough area remains tofacilitate the required interconnections between LEDs where a largenumber of LEDs are used. Certain applications may employ metal coreprinted circuit boards (MCPCBs) to assist in managing the heat generatedby a large number of LEDs. However, many existing designs suffer fromcertain shortcomings, including the ability to include a plurality ofcontrollable LEDs in a narrow or small footprint.

A schematic diagram of one layer of an embodiment of the invention isdepicted in FIG. 1. Light engine 10 may be comprised of a substrate 20,for example, a metal core printed circuit board (PCB) or anothersuitable thermally conductive substrate, that may have aninterconnection layer 22 to facilitate the attachment andinterconnection or coupling of various components in a known manner.Light engine 10 may have a power supply input 50 that may be coupled tothe output of a power supply to provide a source of power to lightengine 10.

Light engine 10 may have a plurality of LED sets 30, 32, 34, 36, 38, and40 coupled between power supply input 50 and a power supply return toallow a current to flow from the power supply through the various LEDsets. Each LED set may be comprised of a single LED or a plurality ofLEDs that may be connected in a number of different configurations. Forexample, each LED set may have a plurality of LEDs connected in seriesbetween power supply input 50 and the power supply return 114 (FIG. 5)as shown in greater detail in FIGS. 3 and 4. LED sets may also havedifferent number of LEDs, depending on, for example, the forward voltageof the LEDs included in the LED set. The number of LEDs in each LED setmay be chosen so that the combined total voltage across each of the LEDsets is approximately equal.

Light engine 10 may also have at least one LED group that may beindependently controlled by control unit 120 (FIG. 5) in certainembodiments of the invention. Each LED group may be comprised of atleast one LED set. The layout of the LED sets in a LED group may varydepending on the particular application. For example, the LED setsmaking up a LED group may be repeated periodically along a length oflight engine 10.

For example, with reference to FIGS. 1 and 7, LED group 150 may includeLED sets 30 and 38. Similarly, another LED group (not shown) may includeLED sets 32 and 40. The LED sets in a LED group may be repeated along alength of light engine 10 periodically depending on the number of LEDgroups employed in the light engine. For example, for a light enginehaving a modulo M architecture with M LED groups, each LED group mayinclude every 1/Mth LED set. With reference to FIG. 1, each LED groupmay include every fourth LED set as four LED groups (not specificallyenumerated) may be employed.

Each LED group may have a return path associated with the LED group tocomplete the circuit to a power supply return 114 in order to allow acurrent to flow from power supply output 112 and through the LEDs ofeach LED group. In order to facilitate the independent control of eachLED group, each LED group may have a separate return path. For example,LED group 150 may have LED sets 30 and 38 that may be coupled betweenpower supply input 50 and return path 80. Similarly, LED sets 32 and 40of a second LED group may be coupled to return path 82. LED sets 34 and36 may be members of different LED groups and be coupled to return paths84 and 86 respectively. LED sets mounted to and coupled together usinginterconnection layer 22 may be coupled to return paths disposed inanother interconnection layer, interconnection layer 24, using layerinterconnection elements, such as vias according to known methods. Forexample, LED sets 30 and 38 may be coupled to return path 80 using layerinterconnection elements 60 and 68. Similarly, layer interconnectionelements 62, 64, 66, and 70 may be employed to connect LED sets 32, 34,36, and 40 to return paths 82, 84, 86, and 82 respectively. Generally,all LED sets in a particular LED group may be coupled to the same returnpath using layer interconnection elements at various points on lightengine 10. Such a configuration allows the LED groups to be controlledindependently as described below. Although, four return paths and LEDgroups are shown in light engine 10 any number of return paths and LEDgroups may be used, for example, eight LED groups may be used in certainapplications.

One particular embodiment of LED set 30 is shown in greater detail inFIG. 3. It should be noted that numerous other configurations may alsobe used without departing from the scope of the invention, includingconfigurations where all LEDs in a LED set are not all coupled togetherin series. A resistor 82 may be coupled between power supply input 50and a plurality of LEDs, for example LEDs 80 a-80 g, that may beconnected in series in layer 22. LED 80 g may also be coupled to layerinterconnection element 60, which may be coupled to return path 80 ininterconnection layer 24 to allow a current to flow from power supplyinput 50 through LEDs 80 a-80 g, through return path 80 to power supplyreturn 114. Other LED sets in light engine 10 may have the same ordifferent configurations depending on the particular application.

Another embodiment of a LED set layout in light engine 200 isillustrated in FIG. 4. Light engine 200 may have a substrate 202, whichmay be a multi-layer metal core printed circuit board, and may have afirst interconnection layer 204. Power supply inputs 250 a and 250 b maybe configured to run adjacent to two edges of substrate 202 in layer204. A plurality of LEDs may be mounted between power supply inputs 250a and 250 b in a variety of configurations. For example, LEDs may bemounted in layer 204 in to parallel rows, parallel columns, diagonally,or in another arrangement. LED sets may be constructed byinterconnecting LEDs from each row in an alternating pattern along thelength of the rows. For example, a LED set may be constructed bycoupling resistor 208 to power supply input 250 a, coupling LEDs 206a-206 g together in series, coupling LED 206 g to layer interconnectionelement 210, and coupling layer interconnection element 210 to a returnpath (not shown) on another layer (not shown) of substrate 202.Similarly, another LED set may be constructed by coupling resistor 212between power supply input 250 b, coupling resistor 212 to LEDs 216a-216 g in series, and coupling LED 216 g to layer interconnectionelement 214. Layer interconnection element 214 may than be connected toa return path (not shown) to complete the circuit.

Light engine 200 may have additional LED sets (not shown) to form aplurality of LED groups. The LED sets in each LED group may be connectedto a separate return path (not shown) associated with each LED group toallow each LED group to be controlled independently. In thisconfiguration, power supply inputs 250 a and 250 b and return pathsshould be of a sufficient width to adequately handle the expectedcurrent, which may limit the width W of light engine 200. It may bedesirable to design light engine 200 so that the length L is muchgreater than the width W so light engine 200 may approximate thedimensions of a fluorescent tube so that existing fluorescentencasements may be more readily modified for use with light engine 200.For example, the length L of light engine 200 may be at least ten timesthe width W. Similarly, it may be desirable to construct light engine200 to have a narrow width of less than or equal to, for example, 1 or 2inches.

It should be noted that the traces to implement power supply input 50and return paths 80, 82, 84, and 86 of light engine 10 should be of asufficient width to accommodate the expected current. For light engineshaving a large number of LEDs the width of the power supply input 50 andreturn paths 80, 82, 84, and 86 may limit the dimensions of the lightengine and number of LEDs that may be mounted in a particular area.Employing a mutli-layer metal core PCB may allow long and narrow lightengines to be designed having a large number of LEDs because a secondlayer may be used for the return paths, allowing more space for powersupply inputs and LEDs on a first layer. Moreover, the use of a MCPCBmay allow a greater density of LEDs to be mounted to the light enginebecause MCPCBs have favourable thermal conduction properties.

A simplified schematic diagram of an embodiment of lighting apparatus100 is illustrated in FIGS. 5 and 6. Lighting apparatus 100 may have apower supply 110 having a power supply output 112 and power supplyreturn 114 coupled to control unit 120. Power supply 110 may be aconstant voltage power supply or alternatively a constant current powersupply in certain embodiments. Control unit 120 may be coupled to lightengine 10 using mated connectors 124 of control unit 120 and connector126 of light engine 10. The mated connectors may be connected togetherto allow power supply input 50, which may be coupled to power supplyoutput 112 to be provided to light engine 10. The connectors may bechosen so that they may be physically connected and designed to minimizethe space between control unit 120, light engine 10, and light engine310 so that these components provide a more uniform light output andminimize any “dark” spots between light engines and provide a compactfootprint for the lighting apparatus.

Connector 124 of control unit 120 may be a female connector adapted tobe physically connected with male connector 126 of light engine 10.Connector 128 of light engine 10 may be a female connector adapted to bephysically connected to male connector 130 of light engine 310. Such anarrangement allows either of light engines 10 or 310 to be physicallyconnected to control unit 120 using connectors 126 or 130 and allowsother light engines to be physically connected to light engines 10 or310. This may increase the modularity of a lighting apparatus comprisinglight engines 10 and 310. In one embodiment, female connectors may bemodel no. 20-9159-005-101-116 or 22-9159-005-101-116 connectors and maleconnectors may be model no. 10-9159-005-101-116 connectors from AVXCorporation of South Carolina, U.S.A.

Similarly, connectors 124 and 126 may couple return paths 80, 82, 84,and 86 between light engine 10 and control unit 10 to provide aconductive path for each return path to power supply return 114. Lightengine 10 may also have a connector 128 adapted to connect to connector130 of light engine 310 so that power supply input 50 and return paths80, 82, 84, and 86 may be coupled between light engines 10 and 310.Light engine 310 may also have a connector 132 that may be coupled toanother light engine (not shown) in a similar fashion to maintainconnectivity of power supply input 50 and return paths 80, 82, 84, and86 between the various light engines. Additionally, more than threelight engines may be coupled together in series and controlled bycontrol unit 120. The coupling together of light engines in a modularfashion to be controlled by control unit 120 may increase theflexibility and decrease the cost of modifying lighting apparatus 100for a particular application. For example, the modular design may reducethe number of SKUs of a manufacturer, which may simplify operations andreduce costs.

Light engines 10 and 310 may have the same or different configurationsof LED groups and sets. Light engines 10 and 310 may be configured tohave the same LED groups coupled to the same return path so that the LEDgroups on both of light engines 10 and 310 may be simultaneouslycontrolled by control unit 120. Alternatively, other configurations ofLED sets and LED groups may be employed in certain applications, notingthat the control unit may be limited to simultaneously controlling LEDsets coupled to each separate return path. Although four return pathsare shown in FIG. 5, any other number of return paths may be used, forexample, eight return paths may be used in certain applications. Incertain embodiments, it may be possible to include four return paths ina light engine having a width of one inch and eight return paths in alight engine having a width of 1.75 inches.

One possible embodiment of control unit 120 is shown in FIG. 6 withdetails of the connectors omitted. Control unit 120 may be configured tocouple power supply output 112 to power supply input 50 of light engine10 to provide a source of power to light engine 10 and other lightengines that may be coupled to light engine 10. Control unit 120 mayalso have a controller 126 connected to switching elements 128, 132,134, and 136 so that controller 126 may selectively activate anddeactivate each switching element to allow a current to flow from powersupply output 112, through light engines 10 and 310, and back to powersupply return 114. More specifically, switching element 128 may becoupled to activation output 130 of controller 126 so that a signal maybe provided from controller 126 to selectively activate switchingelement 128 to allow a current to flow through return path 80. Switchingelements 132, 134, and 136 may be configured in a similar manner toselectively allow current to flow through return paths 82, 84, and 86respectively under the control of controller 126.

Switching element 128 may be implemented as a NMOS transistor having itsgate coupled to activation output 130, its drain coupled to return path80, and its source coupled to power supply return 114. When activationoutput 130 is set to high, the NMOS transistor may allow a current toflow from drain to source and similarly prevent a current from flowingwhen activation output is set to low in a known manner.

Control unit 120 may selectively activate all LED sets connected to eachreturn path independently in this configuration. In embodiments whereall LED sets in a particular LED group are all connected to the samereturn path, each LED group may be controlled independently by controlunit 120. This may allow control unit 120 to provide a separate pulsewidth modulated (PWM) signal to each LED group. The ability to provide aseparate PWM signal to each LED group may reduce the load on the powersupply as certain algorithms may be used by controller 126 to minimizethe current variation by staggering the PWM signal provided to each LEDgroup compared to simultaneously turning on and off all LED groups atonce. One possible algorithm to reduce the variation of the currentsupplied by power supply 110, where power supply 110 is a constantvoltage power supply, is described in U.S. patent application Ser. No.12/624,414 to Briggs which was published May 27, 2010 as U.S. PatentApplication Publication No. 2010/0127632, which is incorporated byreference.

The ability to independently control LED groups may provide a number ofadvantages. For example, light engine 200 may have at least one LED sethaving a different colour or colour temperature from the remaining LEDsets. For example, LEDs 206 a-206 g of a first LED set may be a firstcolour and LEDs 216 a-216 g of a second LED set may be a second colour.These LED sets may be included in different LED groups and be controlledseparately so that the colour or colour temperature emitted by lightengine 200 may be varied by control unit 120. For example, control unit120 may control one LED group so that it has an increased duty cycle toincrease the relative intensity of a particular spectrum of light beingemitted by light engine 200. Alternatively, the PWM signals applied toeach LED group may be offset to adjust the light output from lightengine 200.

In certain embodiments at least one LED from at least two different LEDgroups may be mounted on light engine 10 or light engine 200 to beadjacent to or in close proximity to each other. More specifically, atleast one LED from at least two different LED groups may be mounted sothat the light radiated from these LEDs at least partially overlapsbefore the emitted light reaches optics (not shown) in a lightingapparatus. The lighting apparatus may also be constructed withparticular optics to optimize the mixing of light having differentcolours or colour temperatures according to methods known in the art.This may allow for a more uniform light output from the lightingapparatus while allowing mixing of the emitted light where all or asubset of LEDs from at least two different LED groups have differentcolours or colour temperatures. For example, with reference to FIG. 4,LED 206 a from a first LED group may be mounted adjacent to or in closeproximity to LEDs 216 a and 216 b of a second LED group so that thelight emitted from LED 206 a at least partially overlaps with the lightemitted from LEDs 216 a and 216 b. Similarly, it may be advantageous tointertwine individual LEDs of different LED groups and sets as shown inFIG. 4, where LEDs in each LED set are coupled together from alternatingrows, to optimize the quality of light output from light engine 200 whenthe colour, colour temperature, or other parameters are adjusted.

Alternatively, in certain embodiments of the invention, control unit 120may be omitted and replaced with pass through board 160. In theseembodiments, LED groups may not be controlled independently and aresimply provided with the signal from power supply output 112. Powersupply 110 may provide a continuous power output or in certainembodiments be a switching power supply operable to provide a PWMsignal. Pass through board 160 may be coupled to power supply 110 usingconnector 162 and light engine 10 using connector 164 so that powersupply output 112 may be coupled to power supply input 50 of lightengine 10. Connector 164 may also facilitate the coupling of returnpaths 80, 82, 84, and 86 from light engine 10 to power supply return 114via connector 162. Return paths 80, 82, 84, and 86 may be coupledtogether on pass through board 160 so that a single return path isprovided to power supply return 114. Pass through board 160 may allow alighting apparatus to be constructed in a modular fashion and allows thesame light engine architecture to be used for applications that requirea control unit and those that do not require control. This may reducecosts and simplify the manufacturing process.

Alternatively, a lighting apparatus may be constructed having thefunctionality of control unit 120 or pass through board 160 on the samesubstrate as a light engine. Such a light engine may or may not beadapted to be coupled together with another light engine and becontrolled by the controller mounted to the first light engine. Thismodified architecture maintains a degree of modular architecture and maysimplify the manufacturing process and reduce costs in a similar fashionto that noted above.

A further alternative embodiment, may have control unit 120 located in aremote location or elsewhere in the encasement of a lighting apparatusand connected to at least one light engine via a cable rather than beingphysically connected to one end of a light engine as shown in FIG. 5.For example, control unit 120 may be located below the light engine orelsewhere in certain embodiments of a lighting apparatus. The controlunit may continue to be able to control a plurality of light enginesthat may be coupled together as shown in FIG. 5 in a similar manner.

Another embodiment of the invention may include switching elements thatmay be controlled by controller 126, between power supply output 112 andthe LED groups of light engine 10, instead of having the switchingelements coupled between the return paths and the power supply return114. In this embodiment, separate power supply inputs would be providedto the LED sets of each LED group and all LED sets may share a commonreturn path or use a plurality of return paths. For example, the controlunit illustrated in FIG. 6 could be modified to use the power supplyinput 50 as a return path that would be connected to power supply return114 rather than power supply output 112. Similarly, return paths 80, 82,84, and 86 may be used as power supply inputs to each LED group and becoupled to power supply output 112 instead of power supply return 114.Switching elements may be modified to use PMOS transistors connectedbetween the power supply output 112 and LED groups, with a suitablevoltage divider controlled by a transistor coupled to the gate of eachPMOS transistor, so that each PMOS transistor may selectively allow acurrent to flow through each switching elements depending on the outputof an activation output of controller 126 in a known manner. Such aconfiguration using a second layer to provide power inputs to each LEDgroup may similarly allow a high density of LEDs to be mounted to alight engine.

Moreover, it should be noted that further configurations of the controlunit may be utilized provided each LED group may be independentlycontrolled by the control unit without departing from the scope of theinvention.

When introducing elements of the present invention or the embodimentsthereof, the articles “a,” “an,” “the,” and “said” are intended to meanthat there are one or more of the elements. The terms “comprising,”“including,” and “having” are intended to be inclusive and mean thatthere may be additional elements other than the listed elements.

Of course, the above described embodiments are intended to beillustrative only and in no way limiting. The described embodiments ofcarrying out the invention are susceptible to many modifications ofform, arrangement of arts, details and order of operation. Theinvention, rather, is intended to encompass all such modification withinits scope, as defined by the claims.

What is claimed is:
 1. A lighting apparatus comprising: a plurality oflight engines, each of the light engines comprising: a printed circuitboard; and a first LED group on its printed circuit board coupledbetween a power supply input on the light engine and a first return pathassociated with the first LED group on the light engine; the first LEDgroup comprising at least one LED set comprising a plurality of LEDscoupled in series; and a power source comprising a power supply outputcoupled to the power supply input of each of the light engines and apower supply return coupled to the first return path associated with thefirst LED group of each of the light engines; wherein the first returnpath on at least one of said light engines is coupled to the powersupply return of the power source via the first return path on anotherone of the light engines.
 2. The lighting apparatus according to claim1, wherein the power supply input on at least one of the light enginesis coupled to the power supply output of the power source via the powersupply input on another one of the light engines.
 3. The lightingapparatus according to claim 1, wherein the printed circuit board ofeach of the plurality of light engines comprises first and secondinterconnection layers; wherein the at least one LED set of the firstLED group is mounted to the first interconnection layer on each of thelight engines and is coupled to the first return path in the secondinterconnection layer of each of the light engines.
 4. The lightingapparatus according to claim 3, wherein the first LED group comprises aplurality of LED sets coupled in parallel on each of the plurality oflight engines, wherein each of the LED sets of the first LED group ismounted to the first interconnection layer on each of the light enginesand is coupled to the first return path in the second interconnectionlayer of each of the light engines.
 5. The lighting apparatus accordingto claim 1, wherein each of the light engines further comprises a secondLED group on its printed circuit board coupled between the power supplyinput on the light engine and a second return path associated with thesecond LED group on the light engine; the second LED group comprising atleast one LED set comprising a plurality of LEDs coupled in series;wherein the power supply return of the power source is coupled to thesecond return path associated with the second LED group of each of thelight engines; and wherein the second return path on at least one of thelight engines is coupled to the power supply return of the power sourcevia the second return path on another one of the light engines.
 6. Thelighting apparatus according to claim 5, wherein the first LED groupcomprises at least a subset of LEDs having a first colour temperature,and the second LED group comprises at least a subset of LEDs having asecond colour temperature different from the first colour temperature.7. The lighting apparatus according to claim 6, wherein, in each of thelight engines, at least one of the LEDs having a first colourtemperature from the first LED group and at least one of the LEDs havinga second colour temperature from the second LED group are intertwined onthe light engine.
 8. The lighting apparatus according to claim 6,further comprising an optics section; wherein, in each of the lightengines, at least one of the LEDs having a first colour temperature fromthe first LED group and at least one of the LEDs having a second colourtemperature from the second LED group are mounted so that light emittedfrom the LEDs overlaps before reaching the optics section of thelighting apparatus.
 9. The lighting apparatus according to claim 5,further comprising a control unit coupled between the power source andthe plurality of light engines; wherein the control unit comprises: afirst transistor coupled between the first return path on each of thelight engines and the power supply return of the power source; a secondtransistor coupled between the second return path on each of the lightengines and the power supply return of the power source; and acontroller operable to selectively activate each of the first and secondtransistors to allow current to flow from the power supply output of thepower source through the associated LED group on each of the pluralityof light engines to the power supply return of the power source.
 10. Thelighting apparatus according to claim 5, wherein the printed circuitboard of each of the plurality of light engines comprises first andsecond interconnection layers; wherein the at least one LED set of thefirst LED group and the at least one LED set of the second LED group aremounted to the first interconnection layer on each of the light enginesand are coupled to the first return path and the second return pathrespectively in the second interconnection layer of each of the lightengines.
 11. A lighting apparatus comprising: a plurality of lightengines, each of the light engines comprising: a printed circuit board;and a first LED group on its printed circuit board coupled between afirst power supply input associated with the first LED group on thelight engine and a common return path on the light engine; the first LEDgroup comprising at least one LED set comprising a plurality of LEDscoupled in series; and a power source comprising a power supply outputcoupled to the first power supply input associated with the first LEDgroup of each of the light engines and a power supply return coupled tothe common return path of each of the light engines; wherein the firstpower supply input on at least one of said light engines is coupled tothe power supply output of the power source via the first power supplyinput on another one of the light engines.
 12. The lighting apparatusaccording to claim 11, wherein the common return path on at least one ofthe light engines is coupled to the power supply return of the powersource via the common return path on another one of the light engines.13. The lighting apparatus according to claim 11, wherein the printedcircuit board of each of the plurality of light engines comprises firstand second interconnection layers; wherein the at least one LED set ofthe first LED group is mounted to the first interconnection layer oneach of the light engines and is coupled to the first power supply inputin the second interconnection layer of each of the light engines. 14.The lighting apparatus according to claim 13, wherein the first LEDgroup comprises a plurality of LED sets coupled in parallel on each ofthe plurality of light engines, wherein each of the LED sets of thefirst LED group is mounted to the first interconnection layer on each ofthe light engines and is coupled to the first power supply input in thesecond interconnection layer of each of the light engines.
 15. Thelighting apparatus according to claim 11, wherein each of the lightengines further comprises a second LED group on its printed circuitboard coupled between a second power supply input associated with thesecond LED group on the light engine and the common return path on thelight engine; the second LED group comprising at least one LED setcomprising a plurality of LEDs coupled in series; wherein the powersupply output of the power source is coupled to the second power supplyinput associated with the second LED group of each of the light engines;and wherein the second power supply input on at least one of the lightengines is coupled to the power supply output of the power source viathe second power supply input on another one of the light engines. 16.The lighting apparatus according to claim 15, wherein the first LEDgroup comprises at least a subset of LEDs having a first colourtemperature, and the second LED group comprises at least a subset ofLEDs having a second colour temperature different from the first colourtemperature.
 17. The lighting apparatus according to claim 16, wherein,in each of the light engines, at least one of the LEDs having a firstcolour temperature from the first LED group and at least one of the LEDshaving a second colour temperature from the second LED group areintertwined on the light engine.
 18. The lighting apparatus according toclaim 16, further comprising an optics section; wherein, in each of thelight engines, at least one of the LEDs having a first colourtemperature from the first LED group and at least one of the LEDs havinga second colour temperature from the second LED group are mounted sothat light emitted from the LEDs overlaps before reaching the opticssection of the lighting apparatus.
 19. The lighting apparatus accordingto claim 15 further comprising a control unit coupled between the powersource and the plurality of light engines; wherein the control unitcomprises: a first transistor coupled between the first power supplyinput on each of the light engines and the power supply output of thepower source; a second transistor coupled between the second powersupply input on each of the light engines and the power supply output ofthe power source; and a controller operable to selectively activate eachof the first and second transistors to allow current to flow from thepower supply output of the power source through the associated LED groupon each of the plurality of light engines to the power supply return ofthe power source.
 20. The lighting apparatus according to claim 15,wherein the printed circuit board of each of the plurality of lightengines comprises first and second interconnection layers; wherein theat least one LED set of the first LED group and the at least one LED setof the second LED group are mounted to the first interconnection layeron each of the light engines and are coupled to the first power supplyinput and the second power supply input respectively in the secondinterconnection layer of each of the light engines.